1. Field of the Invention
This invention relates generally to voltage comparator circuits and, more particularly, to a voltage comparator circuit utilizing a level threshold device for controlling the introduction of hysteresis into the circuit.
2. Description of the Prior Art
Voltage comparator circuits are widely used in the electronics field for converting analog voltages into digital representatives thereof. When an unknown analog input signal applied to one input of the comparator crosses a reference threshold voltage, the signal appearing at the comparator output is caused to change state. When the unknown signal is in the vicinity of the threshold voltage, noise may cause the voltage of the unknown signal to vary above and below the threshold voltage causing the comparator output to rapidly switch between two states. This is especially true, for example, in an automotive environment where large voltage transients are not uncommon.
One technique for reducing unwanted switching of the comparator output due to noise is to add hysteresis to the switching circuitry. The introduction of hysteresis into switching circuits for reducing the effect of noise signals and improving noise margin is well-known in the art. For example, co-pending application Ser. No. 31,554 filed Apr. 19, 1979 and assigned to the assignee of the present invention describes a dual slope analog-to-digital converter employing hysteresis. However, known comparator circuits employing hysteresis do not provide the user with complete flexibility with respect to controlling the amount of hysteresis introduced into the circuit including the total elimination of hysteresis.